import re
regex = r"(?<=\bABC\s)(?!.*\bABC\b).*"
s = ("ABC anything about the sky ABC and anything about the moon\n"
"ABC anything about the sky ABC and anything ABC about the moon")
print(re.findall(regex, s))
aW1wb3J0IHJlCgpyZWdleCA9IHIiKD88PVxiQUJDXHMpKD8hLipcYkFCQ1xiKS4qIgoKcyA9ICgiQUJDIGFueXRoaW5nIGFib3V0IHRoZSBza3kgQUJDIGFuZCBhbnl0aGluZyBhYm91dCB0aGUgbW9vblxuIgogICAgICJBQkMgYW55dGhpbmcgYWJvdXQgdGhlIHNreSBBQkMgYW5kIGFueXRoaW5nIEFCQyBhYm91dCB0aGUgbW9vbiIpCgpwcmludChyZS5maW5kYWxsKHJlZ2V4LCBzKSk=