Former Olympic gold medallist Bruce - who split from Khloe's mother Kris Jenner after 22 years of marriage toward the end of 2013 - spent over an hour on the phone to her estranged husband on New Year's Day to keep him in a positive frame of mind.
A source told Hollywoodlife.com: ''He told Lamar to forget about everything that happened in 2013 and not drag all the drama, defeats and embarrassments with him.
''Bruce told him, 'It will eat you alive and ruin any progress if you stay in the past.' He also told Lamar to stay off the websites and turn the TV off and not listen to gossip about him. He basically gave Lamar a lot of advice and mental support.''
Khloé, 30, called time on her four-year marriage to basketball player Lamar, 34, in September after allegations surfaced accusing him of cheating on her with multiple women and using illegal drugs. He is now said to be worried about the way he will be portrayed in the forthcoming series of reality show 'Keeping up with the Kardashians', which centres around Khloe and her sisters Kourtney and Kim.
Bruce reportedly told him to ''hope for the best but expect the worst when it comes to that show and what they're going to reveal because this is how they survive - by putting everything on the table.''
It was recently revealed Khloé is still in contact with Lamar and is determined to help him stay sober, although friends insist they have no plans to reconcile.
The new series of 'Keeping Up with the Kardashians' will air in the US on January 19.
Take a look back at October's inaugural event.
The film is expected to continue without Mendes' involvement.