Rebekah Brooks borrowed her Scotland Yard horse after discussing it over lunch with Britain's top officer, an inquiry heard today.
Former commissioner Lord Blair said he had been dining with the ex-News International chief executive before she called the force's media chief to request the loan.
The Leveson Inquiry into press standards also heard how the teenage sons of two former commissioners were given work experience at The Sun newspaper.
Lord Blair said he had not been behind the leak to press last week that Raisa the horse was taken into Mrs Brooks' care.
He also said he had no recollection of telling Mrs Brooks about a potential loan but accepted evidence from force press chief Dick Fedorcio that she would have found out about it over a lunch.
Lord Blair told the inquiry: "He (Mr Fedorcio) was telephoned by Rebekah Brooks asking about this arrangement - she had heard that this arrangement existed and he arranged for her to go down to see the inspector in charge of horses...
"This seems to have happened on the day that I had lunch with her and, what I understand Mr Fedorcio is going to say, that this was discussed at the lunch. I have absolutely no recollection of that."
Lord Justice Leveson asked the former police chief: "Is this a big deal?"
Lord Blair replied: "No."
He also said "it was a perfectly normal process" to get his 15-year-old son work experience at The Sun.
He said Mr Fedorcio told him previous Met police chief Lord Condon had previously arranged for his child to sample life at News International.
Lord Blair said he told Mr Fedorcio: "Oh well that's the kind of thing that would excite most 15-year-olds, so I think that would be a good idea."
Lord Blair also described how his wife had confronted Mrs Brooks over a headline in The Sun saying "Blair is doomed".
He added: "As I remember, that was the only time I saw Rebekah speechless."
Details of the two-year loan of Raisa the horse were given last month to the Leveson Inquiry but only became public last week - prompting fresh scrutiny over relations between police chiefs and News International.
Mrs Brooks, who resigned last year as chief executive amid the furore over phone-hacking allegations, "fostered" the horse after it retired from active service in 2008.
She paid food and vet bills until Raisa was rehoused with a police officer in 2010, months before fresh investigations began into illegal activities at the News of the World.
The force said the horse - once ridden by the Prime Minister - was returned in a "poor" condition and later died of natural causes.
Mrs Brooks remains on bail after being questioned by detectives, days after resigning last summer, on suspicion of phone hacking and corruption.
Lord Blair was briefed about the Met's phone-hacking investigation before the arrests of News of the World royal editor Clive Goodman and private detective Glenn Mulcaire in August 2006.
But he said he was not given a sense of how widespread the illegal practice was or the likelihood that people other than Mulcaire were also carrying it out.
The former commissioner stressed that he understood former senior Met officer Peter Clarke's decision to restrict the scope of the hacking probe in 2006 at a time when police were tackling a massive terrorist threat to the UK.
But he said he might have done things "slightly differently" if he or his deputy commissioner had been alerted to the large number of phone-hacking victims and the possibility that other journalists were also involved.
He told the hearing: "We might have taken a decision to say, 'OK, we can't deal with this at the moment, but we will hand it over now it no longer concerns the royals to - potentially - the specialist crime directorate for a scoping study in due course'.
"That's a possible set of decisions that could have been made."
Lord Blair only learned after 2006 that his private and official mobile numbers were included in notes seized from Mulcaire by police, the inquiry was told.
He said he had no evidence that his phone was ever hacked, and just put this down to experience.
"I think I just literally said 'Oh, really?' because we were dealing with all sorts of horrors at the time," he said.
"So I just suppose I thought 'Well, two people have been arrested, that's it then'."
The former commissioner criticised the speed of former Scotland Yard assistant commissioner John Yates's response to a July 2009 Guardian report which alleged phone-hacking was far more widespread than previously believed.
Mr Yates began his examination of the claims on the morning the article appeared, and in the late afternoon made a media statement dismissing calls for the Met's hacking investigation to be re-opened.
Lord Blair said: "From what I can see, that decision was just too quick. Why could you not have gone back and with all these allegations looked further into what did the material actually say?...
"I don't quite understand why John took that decision with the speed that he did."
The inquiry also heard that only a small number of junior police officers are likely to be arrested as part of the Met's ongoing investigation into alleged corrupt payments by journalists to public officials, called Operation Elveden.
Lord Blair said: "Before making this statement, I took the precaution of asking in the broadest possible terms with Operation Elveden as to whether my suggestion that I was not likely to see a large number of arrests of colleagues and that those that were arrested were likely to be of junior rank.
"That is the assurance I've been given as of a few weeks ago.
"I find it inconceivable that senior colleagues would be taking money directly in this day and age."