Season 4: Episode 15 - The Stinsons

The Stinsons: After noticing some bizarre and elusive behavior from Barney, the gang starts to suspects that he may have found a girlfriend. When he mysteriously leaves MacLaren’s during drinks they decide to follow him, and they discover that he’s actually been secretly visiting his mother. However, they also discover that Barney has convinced his mother that he’s married and has a son, and that he’d hired actors to portray them. After barging in on Barney with his “family,” the gang has no option but to play along, until Ted gets caught cheating with Barney’s “wife.” Meanwhile, Lily admits to Marshall that she hates his mother, while Robin commiserates with the old soul portraying Barney’s “son.”